A cooling unit for an engine is known in the art which comprises a cylinder head formed with an intake port on one side and with an exhaust port on the other side, a water jacket formed in a cylinder block in surrounding relationship with a cylinder wall which defines cylinder bores and opening into the surface of the cylinder block, a gasket held sandwiched between the cylinder head and the cylinder block to seal therebetween, and a control board on the gasket and inserted into the water jacket.
An example of such a cooling unit for an engine is disclosed in Japanese Laid-Open Patent Application No. 502768/2000, which states that the control board controls a flow of cooling water within the water jacket to achieve an efficient cooling of an engine.
However, if the flow of cooling water within the water jacket is controlled in a manner as disclosed in the cooling unit for an engine of the citation, there still remain the following problem:
A first problem relates to a combustion chamber of an engine where it is recognized that the temperature is higher toward the exhaust port than toward the intake port, and the same is true toward the exhaust port in the cylinder wall.
Thus a temperature difference exists between the intake port and the exhaust port of the cylinder wall, and if the exhaust port is not sufficiently cooled, the cylinder wall toward the exhaust port may be deformed by thermal expansion, leading to an oil depletion caused by a deformation of the cylinder bore or a deformation of the surface of the cylinder block to induce a defective sealing by the gasket.
A second problem relates to a cooling water passage formed in the cylinder block to feed cooling water to the water jacket. Considering a cooling water temperature near the cylinder wall at a location which is adjacent to the inlet of the cooling water passage and at a location away from the inlet, the cooling water temperature is higher at the latter location, and this means that the cylinder wall located away from the inlet is insufficiently cooled in a corresponding manner, whereby the cylinder wall may be deformed by thermal expansion, presenting the problems of an oil depletion and a defective sealing of the gasket.
A third problem relates to a starting of an engine. When the warming up of the engine is not performed, the cylinder bores do not assume a raised temperature, and thus there is no need to cool it by cooling water. However, as the engine is started, the cooling water begins cooling the cylinder wall, and this flow of the cooling water prevents a temperature rise of the cylinder wall, requiring an increased length of time for the warming up of the engine.
It is common that a fuel cost during the warming up is degraded as compared with the fuel cost during a normal operation, and the longer it takes for the warming up, the worse the fuel cost.
With respect to above problems, a cooling unit for an engine according to a first invention which comprises a cylinder head formed with an intake port on one side and with an exhaust port on the other side, a water jacket formed in a cylinder block in surrounding relationship with a cylinder wall which defines cylinder bores and opening into the surface of the cylinder block, a gasket held sandwiched between the cylinder head and cylinder block to seal therebetween, and a control board on the gasket and inserted into the water jacket
is characterized in that the control board is formed to be arcuate in conformity to the profile of the water jacket and is disposed only toward the intake port.
A cooling unit for an engine according to a second invention which comprises a cylinder head formed with an intake port on one side and with an exhaust port on the other side, a water jacket formed in a cylinder block in surrounding relationship with a cylinder wall which defines cylinder bores and opening into the surface of the cylinder block, a gasket held sandwiched between the cylinder head and cylinder block to seal therebetween, and a control board on the gasket and inserted into the water jacket
is characterized in that the control board is formed to be arcuate in conformity to the profile of the water jacket and is disposed toward both the intake port and the exhaust port, a spacing between the control board and the cylinder wall toward the exhaust port being narrower than a spacing between the control wall and the cylinder wall toward the intake port.
A cooling unit for an engine according to a third invention which comprises a cylinder head formed with an intake port on one side and with an exhaust port on the other side, a water jacket formed in a cylinder block in surrounding relationship with a cylinder wall which defines cylinder bores and opening into the surface of the cylinder block, a gasket held sandwiched between the cylinder head and cylinder block to seal therebetween, and a control board on the gasket and inserted into the water jacket
is characterized in that there are a plurality of cylinder bores and the control board is formed to be arcuate in conformity to the profile of the water jacket, the water board being provided toward both the intake port and the exhaust port for each cylinder bore, a spacing between the control board and the cylinder wall for the cylinder bore which is disposed adjacent to the inlet of a cooling water passage which feeds a cooling water to the water jacket being wider than a spacing between the control board and the cylinder wall for the cylinder bore which is disposed away from the inlet.
A cooling unit for an engine according to a fourth invention which comprises a cylinder head formed with an intake port on one side and with an exhaust port on the other side, a water jacket formed in a cylinder block in surrounding relationship with a cylinder wall which defines cylinder bores and opening into the surface of the cylinder block, a gasket held sandwiched between the cylinder head and cylinder block to seal therebetween, and a control board on the gasket and inserted into the water jacket
is characterized in that there are a plurality of cylinder bores, and the control board is formed to be arcuate in conformity to the profile of the water jacket, the control board being disposed toward both the intake port and the exhaust port for each cylinder bore, the control boards disposed toward the intake port for each cylinder bore being connected together and the control boards disposed toward the exhaust port for each cylinder bore being connected together, there being a thermo-valve disposed between the control board disposed toward the intake port which is located adjacent to the inlet of a cooling water passage which feeds a cooling water to the water jacket and the control board disposed toward the exhaust port to open when the temperature of the cooling water has risen to a given value.